Sorption and diffusion of 14C-atrazine through isolated plant cuticles

Sorption and penetration of atrazine through plant cuticles were investigated using enzymatically isolated tomato and pepper fruit cuticles. Sorption was rapid and equilibrium was reached within 4 – 6 hours for the two species. Mean values for cuticle/water partition coefficients (Kcw) were 140 and 131 for pepper and tomato cuticles, respectively. Sorption was not affected by pH solution between 3.5 and 8 but it was reduced at pH 1.7. The amount sorbed (nmol mg−1) varied linearly with concentration from 1.3 μM to 0.1 mM. Atrazine was reversibly sorbed to cuticles and only 1 to 4% was still retained by cuticles after 48 hours washing. Diffusion of atrazine through cuticles increased linearly with time. Permeability coefficient values determined at 0.1 mM atrazine were 24.6 and 47.3 nm s−1 for pepper and tomato fruit cuticles, respectively. Comparison with simazine showed that the cuticle/water partition coefficient was markedly lower for this herbicide. Kcw was 48.4 and 46.2 for pepper and tomato cuticles, respectively. Diffusion of simazine through cuticles was also lower particularly for pepper cuticles.